Porous plastic film



Nov. 9, 1965 I c. A. FELDT ETAL POROUS PLASTIC FILM 2 Sheets-Sheet 1 Filed Dec. 5. 1960 FIG.|

INVENTORSZ RLES A. FELDT LIAM G. JAMES MORRIS MINDICK MW, M

v-QJV- ATT'YS Nov. 9, 1965 Filed Dec. 5, 1960 FIG. 4

C. A. FELDT ETAL POROUS PLASTIC FILM THERMOPLASTIC IN WARM POLYMER DISSOLVED BUTYROLACTON E 2 Sheets-Sheet. 2

FILTER POLY POLA R POLYMER DISSOLVED BUTYROLACTONE LINEAR IN WARM MIX-AND HEAT FILTER VACUUM DEAERATE CAST LAYE R OF SOLUTION CONTACT LAYER WITH WATER OR METHANOL DRY FIG. 5

POROUS PLASTIC PERFUME ALCO H OL BATH DRY

INVENTORS: CHARLES A. FE LDT WILLIAM. G. JAMES MORR MINDICK United States Patent O 3,216,882 POROUS PLASTIC FILM Charles A. Feldt, Naperville, William G. James, Lockport, and Morris Mindick, Chicago, Ill., assignors to Nalco Chemical Company, Chicago, 111., a corporation of Delaware Filed Dec. 5, 1960, Ser. No. 73,690 6 Claims. (Cl. 161-109) This invention relates to porous plastic compositions which have a plurality of pores extending throughout or perforating at least one dimension of said compositions.

In a particular embodiment of the invention the pores are restricted near at least one outer surface of the plastic compositions which are most advantageously formed into films or sheets.

A special embodiment of the invention consists in the provision of porous plastic compositions of the type described, having pores which contain amounts of perfume. The perfume bearing pores render the composition fragrant for long periods of time. Pore walls may have composition and structural configuration permitting the release of fragrance under controlled physical or chemical conditions.

In a further particular aspect of the invention, there is provided an improved fuel cell of the ion membrane type wherein improved electrical, chemical and physical properties are achieved.

Perfumes are voltale, aromatic materials which are pleasing to the olfactory senses. Due to their volatility, their fragrance soon disappears when applied to various types of solid and semi-solid surfaces such as fabrics, human skin and hair, glass, wood, and the like. Many attempts have been made to provide slow-release, long lasting fragrances, but such attempts have only met with moderate success. In the perfume art it is customary to employ fixatives with perfume formulas to prolong their effect. Such fixatives frequently work by reducing the rate of evaporation of the perfume. However, this phenomenon also tends to reduce the number of odoriferous particles in the air at a given time, thereby making the perfume flat and lifeless.

Attempts have been made to use solid perfume-carriers which lock in fragrance to a certain extent, and slowly release it over a period of time. Illustrative of this is the treatment of a porous cellulosic material such as blotting paper with a perfume. The scent is released for a period of a few days or several weeks, and at the end of this time expended.

There are numerous applications in both the domestic and industrial areas where it would be of benefit to provide various types of compositions in the form. of plastic sheets, films, blocks or rods which would be capable of releasing pleasant fragrances over prolonged periods of time. Such products, for example, if in the form of clear or colored sheeting, could be employed as novelty packaging materials which would have wide appeal to purchasers of a variety of products. Several such areas that immediately suggest themselves would be outer packaging or covering materials for such products as perfumes, colognes, soaps, and other similar toilet preparations. If such packaging materials were capable of emitting a scent similar to the scent of the material contained within the package, scented products could be sealed at the factory, and customers contemplating purchasing the packaged item could determine its odor by snifiing the fragrance emitted from the scented wrapping.

In another vein, a perfume-containing object of the type described, if formed into solid objects, could be employed in the manfacture of various types of jewelry ice such as earrings, bracelets and pins. The jewelry would slowly release a pleasant odor, thereby materially enhancing its esthetic value.

In still another vein perfumed porous plastic objects could be either formed or applied as a film to such toiletry articles as hairbrushes, combs and manicure devices, which when used would impart a pleasant fragrance to the hands and hair of the user.

In a specialized field of utilizing perfumed porous plastic sheets, it would be possible to prepare clear or opaque plastic sheeting which could be applied to such surfaces as walls, ceilings, and floors to impart pleasant fragrances to rooms or other similar living or working areas.

Another application where slow-release perfume containing plastic substances would be of esthetic benefit would be their empolyment in air filtering systems for homes and industrial buildings. In the case of domestic heating units of the forced warm air type it would be possible to employ minor amounts of the porous perfume releasing plastics in combination with conventional air filters whereby scented air would be slowly and uniformly released throughout the rooms serviced by the filter.

In addition to the above suggested applications for scented porous plastics, several other uses are immediately apparent such as linings for dresser drawers, garment bags, and the like.

In recent years a great deal of research has been directed to the perfection and commercial adaptation of fuel cells. In the current book, Fuel Cells, by G. J. Young, Reinhold Publishing Corporation, 1960, a fuel cell is defined as an electrochemical device in which the chemical energy of a conventional fuel is converted directly and usefully into low voltage direct current, electrical energy. In this book several types of basic fuel cells are described.

One of the newer type fuel cells which has received a great deal of attention is the so-called ion membrane fuel cell. This type of fuel cell operates using hydrogen and air as the fuel and employs a so-called solid electrolyte in the form of a porous membrane. Several advantages which have been attributed to ion membrane fuel cells, are summarized in the publication Some Plain Talk About Fuel Cells, published by the General Electric Corporation. These advantages are said to be:

(1) Operates on either oxygen or free air.

(2) Operates at room temperature and normal pressure.

(3) No caustic liquid electrolyte to handle, pump or contain.

(4) Silent operation. Nothing to wear out. No noxious exhaust.

(5) Can operate at zero gravity. Highly shockand vibration-resistant.

(6) Self-regulating. Fuel is consumed only on demand. No external control of fuel flow required.

(7) Easily reversible. An electric current applied to the cell will electrolyze water, producing fuel for later use. This permits energy storage from a solar generator.

(8) High power-to-weight and power-to-volume ratios. Prototype cells produce about 25 w./ft. at 0.5 v./cell (maximum power point). A 30-cell battery with IOO-Watt peak capacity will produce 850 w./ft. at maximum power.

(9) High fuel efficiency gives high energy to fuel weight ratios. Thermal efiiciency is 677V percent where V is the voltage of a single cell. Thus, at 0.82 volt, the efficiency is 55 percent; giving fuel consumption rate of 0.1 lb. H /kw. hr. and 0.8 lb. O /kw. hr.

One of the major disadvantages in the ion membrane fuel cell resides in the chemical and physical characteristics of the membrane used to separate the porous electrodes. In most cases conventional membranes, when used in fuel cells of this type, tend to undergo an expansion when they are wetted with water. Similarly, they tend to contract when moisture is removed and drying conditions prevail. These expansion and contraction characteristics tend to materially hamper the electrical efliciency of the fuel cell, both from the standpoint of fuel leakage and overall operating efficiency. In some instances it has been observed that conventional membranes tend to provide a sufficiently high ohmic resistance whereby capacitance effects are observed.

It would be of benefit to the art if an improved porous conductive film were available for use in ion membrane fuel cells which would not be subject to the deficiencies described above. In therefore becomes an object of the invention to provide a new type porous membrane for utilization in the construction and operation of ion membrane fuel cells.

Another object is to provide improved fuel cells of the ion membrane type which utilize in their construction highly conductive porous membranes.

A further object is to provide new porous plastic compositions which have a plurality of pores extending through or perforating at least one dimension of said composition.

A still further object is to provide porous plastic compositions which are capable of containing perfume and which will slowly release perfume over prolonged periods of time, or which may be caused to release pleasant fragrances by predetermined varying physical and ehemical conditions.

An important object is to provide a method of making new types of porous plastic objects whereby the porosity may be controlled by using variations in manufacturing technique.

A special object of the invention is to provide novel porous plastic compositions which have pores extending throughout or perforating at least one dimension with said pores each being restricted near at least one junction with an outer surface of the plastic composition.

A specific object correlated with the prior object is to provide porous films or sheets which have pores having restricted openings near their junction with either one or both sides of such sheets.

For a more comprehensive understanding of the several concepts of the invention, reference may be had to the drawings of which:

FIGURE 1 is a vertical cross-sectional schematic view of a ion membrane fuel cell showing the utilization of a porous plastic composition of the invention in combination therewith;

FIGURE 2 is a horizontal fragmentary cross-sectional view of a porous plastic film of the invention showing a typical pore arrangement which occurs within such film;

FIGURE 3 is an enlarged diagrammatic cross-sectionalview taken across typical pore 56 of FIGURE 2, showing a cross-sectional view of a pore which has been treated with perfume;

FIGURE 4 is a simplified flow-sheet showing a typical manufacturing method for producing the preferred porous plastic compositions;

FIGURE 5 is a flow-sheet similar to FIGURE 4 showing a typical arrangement for treating the porous plastic compositions with perfume;

In accordance with the invention, it has been found that novel porous plastic compositions may be provided by dissolving 40-90 percent by total solute weight of a water insoluble, acid and alkali resistant thermoplastic polymer and from -60 percent by total solute weight of a substantially linear polypolar polymer, into a single common polar organic solvent. This solution is then formed into a shaped object under specific conditions which will be set forth later. The shaped object is then contacted with water for a period of time sufiicient to displace the organic solvent from the shaped object and set its shape. After the treatment with water the object may then be dried if necessary, at temperatures below about 300 F. for a period of time sufficient to remove substantially all the water therefrom. The above process starts with preparation of an organic casting solution which may be varied both as to ingredients and concentration to provide a variety of finished products which are then subsequently treated in accordance with the above described process. The ingredients of the casting solution are described more fully in the following sections.

THE COMMON POLAR ORGANIC SOLVENT To be operative, it is necessary that the organic solvent employed be both a solvent for the water insoluble, acid and alkali resistant thermoplastic polymer as well as the polypolar polymer. In addition to being a common solvent for these two resinous chemicals, it is beneficial that i the solvent be capable of providing a total solution concentration of at least 10 percent and up to as high as about 30 percent or more by weight. Since the two polymers placed into the solvent are apposed in their chemical structure and properties, not all organic solvents are capable of acting as solvents for both of them.

It has been found that a particular class of organic solvents is capable of dissolving both the thermoplastic polymer and the polypola-r polymer to provide solutions within the concentration ranges specified. Generally, those organic solvents which have a dipole moment in excess of 3.0 and preferably in excess of 4.0 are admirably suited for dissolving the polymers at relatively high concentrations. Solvents of this type are illustrated by such materials as cyclopentanone, tetramethylene sulfone, dimethyl sulfone, dimethyl acetamide, dimethyl formamide, N- acetyl morpholine, gamma butyrolactone, and propylene carbonate. Of these typical solvents, gamma butyrolactone has proven itself to be superior both from the standpoint of its solvency powers, and commercial availability. In addition to possessing a high dipole moment, the solvents should posses a low hydrocarbon to polar group ratio, as well as having little or no self-hydrogen bonding power. For a detailed description of solvents of the type discussed, in relationship to their dipole moments and solvency for certain plastics, reference may be had to The Properties of Nitrile Binary Systems and Their Relation to Polyacrylonitrile Solubility, by M. K. Phibbs, J. Phys. Chem., 59, 346353 (1955).

THE THERMOPLASTIC POLYMER The thermoplastic used in the present invention may be of several types, both as regards chemical structure and physical properties. The thermoplastic material should be capable of being formed into homogeneous films or other shapes from an organic solvent casting solution. These films or shapes should be chemically stable, resistant to acids and alkalies, and water insoluble, in order to ultimately provide a satisfactory composite product. The thermoplastic polymer must also be compatible when dissolved or dispersed in a casting solution with the polypolar polymer which is incorporated therewith at the time the article is formed.

The most useful type of thermoplastic polymer materials are those derived from the copolymerization of vinyl chloride and acrylonitrile. These polymers may range from between 45 percent and percent by weight of vinyl chloride, preferably, between 60 and 80 percent vinyl chloride, the balancing being acrylonitrile. Their specific viscosities at 20 C. are preferably from 0.2 to 0.6 (0.1 gram in 50 cc. acetonyl acetone). Such polymers are described in US. Patent No. 2,520,565. A typical polymer of this type is a commercial material sold under the trade name Dynel. This material contains a major portion of vinyl chloride and a minor portion of acrylonitrile and varies somewhat in its constituents from batch to batch as manufactured. The material, as supplied in its filament or fiber form; has a specific gravity of 1.31 at 8l F., a tenacity (wet or dry) of 2.5-3.5 grams per denier and a 42 to 40 percent elongation (Wet or dry). The material is soluble in acetone, cyclohexanone and dimethylformamide. It has a strain release beginning at 240 F. and a softening range between 300 F. and 325 F.

Polymers containing vinylidene chloride and vinyl chloride ina percent by weight of about 90to 10 percent, and copolymers of vinylidene chloride and acrylonitn'le are also useful. Another type of useful polymer is the copolymer produced by the copolymerization of polyvinyl alcohol and butyraldehyde. This latter copolymerization produces polyacetals whose film-forming properties, when reacted under proper conditions, are similar to those indicated for the vinyl chloride-acrylonitrile polymers. However, homopolymers produced by the polymerization of acrylonitrile', vinyl chloride and vinylidene chloride are also contemplated.

The above listed polymers are only indicative of the general class of polymers that may be employed. The types of polymer that are useful are necessarily limited to those which are relatively water insoluble, chemically stable, and acid and alkali resistant. Choice also is limited 6 When crosslinking is present in the molecule, it will never exceed more than 2 percent by Weight. Insofar as molecular weight is concerned, the polymers should have a minimum average molecular weight of between 1,000- 5,000 with a preferred average molecular weight being at least 10,000 or more.

Typical anionic polymers suitable for preparing the porous plastic compositions are those polyelectrolytes which contain as their functional groups, such radicals as carboxylic acid radicals, phosphonous and phosphonic acid radicals, and sulfonic acid radicals. The preferred type polymers are those water soluble polymers derived by the sulfonation of linear polystyrene.

Other types of anionic linear polymers that may be employed are those possessing properties of metal chelation. They are generally derived from the condensation of two monomers to produce a structurally amphoteric copolymer. Examples of such polymers would be those described in U.S. Patent 2,564,092.

The chelate polymers may have one or more of the following chelate donor groups incorporated in their structure, either as a side chain group or as part of the chain:

R-NH

THE POLYPOLAR POLYMERS The polypolar polymers may be divided into three separate categories. In one instance, the polypolar polymers are anionic polyelectrolytes while in another instance, they are cationic polyelectrolytes. In a third instance, the polypolar polymers contain a plurality of substantially non-ionizable groups such as where R is from the group consisting of hydrogen and lower alkyl groups. It is thus evident that the polypolar polymers are comprised of polymers which have either positive charges, negative charges, or many non-ionizable hydrophilic groups. All of the above described polymers are substantially linear, and have little or no crosslinking.

The polymers forming chelate compounds are likewise linear and substantially free from crosslinking.

The preferred cationic polyelectrolytes have as their functional group a quaternary ammonium nitrogen atom. This nitrogen atom is preferably attached to the polymer by being associated or linked with an aromatic nucleus which is a side group in the linear chain. Use of the expression associated with the aromatic nucleus is meant to include nitrogen atoms which (A) are a part of the aromatic nucleus, e.g., poly-N-methyl, 2-vinyl-pyridinium iodide and poly-N-vinyl imidazole methyl iodide; (B) are directly attached to the aromatic nucleus, e.g., polystyrene 0- and p-trime'thyl ammonium diodide; and (C) are attached to the aromatic neucleus by a divalent hydrocarbon radical, e.g., poly (vinyl benzyl trimethyl or triethyl ammonium iodide).

In addition to polymers containing a nitrogen atom associated with an aromatic nucleus, quaternized poly- N-vinyl amines and the poly-N-allyl amines may also be used. In the case of these latter compounds, care must be used in preparing the quaternary derivates so that little, if any, crosslinking occurs.

Other polyamines of the type described above may be used, wherein the functional nitrogen atoms are in the form of primary, secondary, or tertiary amino groups convertable to the salt form. Additional useful polyamines are those described in the above referred to U.S.

7 Patent 2,625,529, particularly columns and 7. Other onium polymers as well as condensation polymers such as the alkylene imine polymers e.g., poly-N-methyl polyethylene imine may also be used as the cationic polyelectrolytes.

The polypolar polymers that give most satisfactory results are primarily homopolymers derived from the polymerization of one olefinic compound. For example, a poly-(vinyl benzyl trialkyl ammonium salt) and a poly- N-vinyl imidazole alkyl salt give superior results.

In a preferred embodiment of the invention, poly(vinyl benzyl trimethyl ammonium halide) is used, prepared for example by the chloromethylation and subsequent amination with trimethylamine of polystyrene in known manner. The preferred halide is the iodide.

Other preferred polypolar polymers are the non-ionic polypolar polymers of the type generally described previously. Specific examples of polymers of this type are such polymers as polyvinyl alcohol, polyacrylamide, polymers of N-vinyl pyrrolidone, and certain water soluble copolymers of polyvinyl acetate. Of these particular polymers, poly-(N-vinyl pyrrolidone) is most preferred since it is capable of imparting a high degree of porosity to the plastic compositions.

Both the water-insoluble, acid and alkali resistant thermoplastic polymers and the polypolar polymers are polyvinyl type polymers; e.g., those derived by addition polymerization of at least one mono olefinic compound through an unsaturated aliphatic group. They are preferably addition polymers of the substituted ethylene class, comprising polymers obtained by the polymerization or copolymerization of monomers containing a CH2=& group.

PREPARATION OF THE POROUS COMPOSITIONS In US. Patent No. 2,957,206 there are described methods for making ion selective membranes. In this patent the polyelectrolyte type polypolar polymers and thermoplastic polymers are described in detail and are shown as being dissolved in the solvent, gamma butyrolactone. These solutions after appropriate treating steps are cast into films, dried, and then treated with certain solvents to produce anion or cation exchange membranes. Much of the technology described in Mindick et al., US Patent No. 2,957,206, is pertinent to the preparation of the solutions used in preparing the products of this invention.

The technology described in Mindick et al. is pertinent insofar as the concentrations and proportions of the ingredients used to prepare the casting solutions are similar to those used in preparing the products of this invention. Thus, the polymer content of the solution may be any amount up to about 30 percent by weight of the solution, above which value the viscosity becomes excessive. The higher concentrations are preferred for commercial production, and the ability to provide a concentrated solution is very advantageous for producing porous plastic products. Concentrations of 30 percent are preferred. The most preferred concentration is on the order of 20 percent.

The proportion of the polypolar polymer in the mixture of polymers is at least 10 percent and preferably up to 30 percent, and at times as high as 60 percent by weight of the polymer mixture. The proportion of the thermoplastic polymer is thus about 40-90 percent, preferably 70-90 percent by weight. Especially valuable products are produced with a minor proportion of between and 30 percent by weight of polypolar polymer contained therein. The casting solution preferably contains about 9-15 percent of the thermoplastic polymer and about 1-15 percent of the polypolar polymer, by weight of the solution.

In the preferred practice, the polymers are dissolved in gamma butyrolactone. In the production of these solutions, small gel particles were observed in films cast therefrom. It was discovered that the thermoplastic polymer contained these particles, and that they could be elminated by separately dissolving and then filtering the polymer. Preferably, vigorous agitation and tempertures of at least about to about 300 F. are employed for dissolving the thermoplastic polymer, prior to filtration. The polypolar polymer is dissolved separately in the lactone, and the two solutions are mixed for casting. Preferably, the solutions are mixed at a temperature of not greater than 180 F., filtered, and deaerated just prior to forming the objects to be produced.

The casting solutions thus described are eminently suitable for the production of film or sheeting products representing the preferred physical form of the plastic objects of the invention. In the case of large scale production, the casting solution may be conveniently formed into films by casting the solution on a continuous belt whereas in the case of producing small quantites of film like material, the casting solutions may be cast upon metal plates, sheets of glass or solvent resistant plastic. After the films have been cast, they are then treated with water, methanol, or any other solvent for the polypolar polymer which does not dissolve or swell the thermoplastic polymer. This tends to produce the novel pore like structure in the composition.

The preferred pore producing treating agent is water. The films are most preferably contacted with a pore producing bath immediately after they are formed or cast, so that substantially none of the casting solvent is lost by evaporation. This step of forming a film and then treating with water or other pore producing agent, without the loss of casting solvent represents one of the more novel and critical processing steps of the invention. The temperature of the water used to treat the cast films may be varied between 32 F. and not more than about 210 F. The amount of time that the water contacts the cast object may vary from as little as one minute to as long as 24 hours. Other temperatures and times, may of course be preferred where other pore producing reagents are used.

The films, if cast on metal plates, and then immersed in water will expand from one to four times in thickness. The surface of the film contacting the metal casting surface will tend to be highly irregular and rough whereas the surface exposed to the water is very smooth and uniform and is extremely pleasant to the touch. When it is desired to produce a film that is smooth on both sides, it is necessary that the film be removed from the casting surface shortly after it has contacted the water. This removal is possible since the water tends to coagulate and permanently set the film into a unitary solid sheet which may be handled. Satisfactory films can also be produced by extruding fiat or tubular film directly into water without using a plate or belt.

The water treatment tends to displace the organic solvent from the cast film and is believed further to produce a coagulating effect on the thermoplastic polymer contained in the film. The most satisfactory films are prepared by casting films having thicknesses between 0.2 and 15 mils. When films of this thickness are treated with water, the solvent is readily displaced within a relatively short period of time. When thicker films are prepared, the time, required for the water to remove the solvent from the film is substantially increased and also it is difiicult to maintain the physical shape and dimension of the initially cast film due to the presence of the solvent.

When it is desired to produce porous plastic composi tions, having structure and shapes other than that of films, it is possible to form such objects by mold casting the casting solutions, as well as by extrusion into the pore producing bath. When the mold technique is used, it is necessary to inject water or other pore producing treating agent into the mold to impart sufiicient rigidity to the object. The object may be then removed from the mold and further treated with said treating agent to provide suitable pores through and throughout the surfaces of the article. As a further aid for understanding the invention, typical casting solutions are presented below in Table I.

Another method of sealing the pores is to coat the surface of the film with a small amount of a solvent of the type used in casting or forming the film. This has the effect of dissolving a certain amount of the surface Abbreviations Used:

Dynel-60% olyvinylchloride and 40% polyvinylacrylonitrile. VYNS-3-90 a polyvinylchloride and 10% polyvinylacetate. P.S.A.Polystrene sulfonic acid. L.S.B. R.Poly-vinyl-benzyl-trimethyl-ammonium iodide. P.V.P.Polyvinylpyrrolidone. P.V.I.Po1yvinyl imidazole-methyl-iodide. G.B.L.Garnma butyrolactone. D.M.F.Dimethylformamide.

For a more comprehensive understanding of the method of making the preferred porous films of the invention, a reference should be made to FIGURE 4 which is a flow sheet showing the stepwise typical processing of raw ingredients into finished porous plastic film.

The compositions produced in accordance with the flow sheet shown in FIGURE 4 comprise porous plastic compositions having pores extending throughout or perforating at least one dimension of said composition. These pores are singularly unique in that they are restricted near an outer surface of the composition. Assuming a typical composition of the invention to be a film, the concept of these novel pore forms is shown in FIG- URE 2.

The film shown in FIGURE 2 is represented generally by the numeral 38. The film has two surfaces or sides 40 and 42. Extending substantially perpendicular to said sides are a plurality of pores designated by the numerals 44a}, 17, c, and d respectively. If the film is cast on a solid surface such as a metal sheet and then contacted with an aqueous bath without removal from the sheet, a pore structure corresponding to 44c is produced. It should be noted that in pore 44c the cross sectional size or diameter is not uniform. The top 48 of pore 44a is restricted near side 40 of the sheet, while the bottom portion 50 of the pore is of substantially larger cross sectional size near side 42 of the film 38 where it contacted the plate. When the film is removed from the plate shortly after it has contacted the aqueous bath, a pore corresponding to 44d is formed having a top 52 and a bottom 54 which are both of relatively narrow dimension with respect to the dimension of the pore located within the central region of the film.

The walls of a typical pore, represented by numeral 56 are relatively smooth. When the film is formed from an anionic polyelectrolyte, the wall surfaces will have 'dis tributed thereabouts, a plurality of anionic groupings such as for instance, sulfonic acid groups.

After the films or other for-med objects have been treated with water 'or other pore producing agent and then dried, it is possible to change the outer surfaces of the pores to effect a closure thereof by applying heat to the surfaces of the film or particular article formed. In the case of films it is possible to close the pores after the film has been dried by using such means as heated calendaring rolls, hot air, and the like. When such heat treatments are used it is preferable that the temperature applied to the face or faces of the films does not exceed 300 F. Temperature should most preferably be maintained within the ranges of 150 and 250 F. for between 0.1 and 10 minutes.

plastic which tends to act as a restrictive covering over a portion of the surface of the pores. Conversely, subjection of the films and other products of the invention to mechanical forces such as direct presure or abrasion will cause pore dimensions to be extended or enlarged. This effect of opening or closing the pores by either chemical of physical phenomena is of extreme importance in connection with the utilization of these films as carriers for perfumes. This release or controlled capture of perfume will be more fully explained hereinafter. v

To illustrate the preparation of typical porous films of the type described above, the following are presented by way of example.

Example I Dynel fiber was dissolved in gamma butyrolactone to provide one part by weight of Dynel to four parts by weight of butyrolactone. The solution was then heated to a temperature of about 200 F. and maintained at that level with vigorous agitation for 2 hours. A homogeneous solution Was produced. Using a similar mixing procedure, one part of polystyrene sulfonic acid was dissolved in 4 parts of gamma butyrolactone and heated to F. until complete dissolution occurred. 23 parts of the polystyrene sulfonic acid solution were then mixed with 77 parts of the Dynel solution, heated to F., vacuum deaerated, and filtered. A small portion of this solution was then poured onto a stainless steel plate and then drawn into a film using an 8 mil doctor blade. The drawing was done at room temperature. The drawn film and plate were then emmersed in a bath of Chicago tap water for 30 minutes, At the end of this period the plate was removed and the film was easily stripped therefrom. After drying at room temperature for 2 hours, an examination of the film showed the surface which contacted the metal casting plate to be irregular and, in some areas, partial 'crenulations seemed to be visible. The other surface, which faced the water, was extremely smooth, and was soft and pliable to the touch. A cross section of this film examined under a microscope showed it to have a pore structure similar to that represented by pore 44c in FIGURE 2.

Example 11 Example I procedure was followed except that the film was stripped from the casting plate about 2 minutes after it had contacted the bath of water. After drying, the film was smooth on both surfaces. A microscopic examination of the film revealed the pore structure to correspond generally to that illustrated by pore 44d in FIGURE 2.

In both Examples I and II, the average interior diameter or size of the pores was about 50 millimicrons, with the smooth face surfaces having pore openings 80 percent smaller than this average, i.e., about 10 millimicron size.

Example III Example I procedure was followed except that the solution was poured on a 150 mesh stainless steel screen and drawn into a film using an 8 mil doctor blade. Another 150 mesh stainless steel screen was placed over the film so that a space of 17 mils existed between the second screen and the film, and said other screen was then fixed in that position. The assembly was immersed in water for 20 hours after which the screens were stripped from the film. After drying the film was smooth on both surfaces. Microscopic examination revealed the pore structure to correspond to that illustrated by pore 44d in FIGURE 2.

Example IV A 20 percent solution which comprised 33 percent by weight of polyvinylpyrrolidone and 67 percent by weight of polyvinyl chloride was made up in gamma butyrolactone which had been heated to about 150 F. to facilitate dissolution. The solution was cast on a stainless steel plate and drawn to a 12 mil thickness with a doctor blade. The plate was then immersed in water for 18 hours and then stripped therefrom. After examination of the film it was observed that the finished article was similar to the film produced in Example I. It had a surface area equal to 19 MF/gm. and pore volume of .04 ml./gm.

The pore sizes of the objects produced by means of the above outlined techniques are dependent upon two variables, namely, the quantity of polypolar polymer in the finished article, and its initially formed thickness prior to treatment with water. With particular reference to films, those films having larger initial thickness and larger content of polypolar polymer, will have pores of greater average cross-sectional size than thinner films having a lesser amount of polypolar polymer. It has also been observed that the utilization of polypolar polymers of the non-ionic type such as N-vinyl pyrrolidone polymers and polyacrylamide polymers, will produce larger pores than will corresponding amounts of either anionic or cationic polyelectrolytes. From this discussion it is evident that the pore size of the film or other objects prepared in accordance with the invention may be varied by controlling either the thickness of the initially cast object, the amount of polypolar polymer used and to some extent, the type of polypolar polymer used in preparing the initial casting solution.

SCENTING THE FILMS As mentioned above, one of the novel characteristics of the films of the invention is that they may have incorporated in their pores, perfumes whereby long lasting fragrance phenomenas may be achieved. To this end, it is possible to take films as produced in accordance with Examples I, II, III and IV, and immerse them in dilute alcoholic solutions of perfume. This procedure is outlined in FIGURE of the drawing. Perfume is imbibed into the pores of the films where it may be physically or ionically bonded into the pore structure. The temperatures of the perfume solutions may vary between their freezing points and their boiling points.

Perfumes are not usually a single chemical ingredient, but are most commonly composed of a variety of materials. Typical ingredients may be generally described as follows: (1) essential oils consisting of volatile oils found in plants and obtained by steam distillation or by other methods; (2) absolute oils extracted from flowers by volatile solvents; (3) natural extractives or soluble resins, extracted with volatile solvents from gums, resins, balsams, beans, etc.; (4) animal products obtained from glands or the secretions of glands of certain animals. Examples are musk, tonquin, civet and castoreum; and (5) aromatic chemical reagents (a) isolates which are definite compounds isolated from essential oils; and (b) synthetics which are produced partially or completely by chemical synthesis.

Since most of the films and other porous structures produced in accordance with the invention have interior pore sizes ranging between about 5 or 10 millim-icrons up to as high as 1,000 microns, with typical pore structures usually having cross-sectional sizes greater than 200 millimicrons, it is possible to easily entrain within the pores quantities of dilute perfume solutions such that the finished product will contain from .01 to 10 perc nt by weight of perfume. The best perfume containing films have thicknesses ranging between 8-22 mils. Satisfactory films may, however, be as thin as 1 mil in thickness and as heavy as mils thick.

Since most perfumes include a variety of chemical components which contain a plurality of functional ionic groups, it is possible to select either anionic or cationic perfume ingredients which will ionically bond to the anionic or cationic polyelectrolyte groupings which are dispersed about the pore walls. In the case of perfume ingredients which contain polar groupings, it is possible to employ hydrogen bonding or Zwitter ion effects to semiperrnanently lock the perfume ingredients into the pores.

Typical ingredients that may be used in preparing perfumes are the following well known chemicals: n-octyl alcohol, n-decyl alcohol, n-undecylenyl alcohol, geranyl acetate, citronellol, linalyl acetate, cyclic (terpenoid)-terpeneol, l-menthol, benzyl acetate, benzyl sa'licylate, phenylethyl acetate, cinnamyl alcohol, methylphenylcarbinyl acetate, dimethylbenzylcarbinyl acetate, nonyl aldehyde, undecylenylaldehyde, methylnonylacetaldehyde, hydroxycitronellal, benzaldehyde, hydratropaldehyde, cinnamaldehyde, vanillin, B-ionone, civetone, irone, acetrophenone, methyl fi-naphthyl ketone, eugneol, safrole, yara yara, methyl benzoate, phenylacetic acid, cinnarnic acid, isoamyl silicylate, ethyl methylphenylglycidate, coumarin, -undecalactor1e (peach aldehyde or aldehyde C-14) ambrettolide, Skatole, methyl methylanthranilate, musk ambrette, p-bromostyrene, and trichloromethyl phenylacetate.

Example V A typical treatment of the films of the invention to place perfume within their pores, may be generally accomplished as follows: a 1 percent by weight of isopropanol solution of a rose perfume having the following ingredients was prepared.

Benzophenone 6 Essence of styrax, F.F.S. 4

A dried film corresponding to the film produced in accordance with Example IV was immersed in the above solution for minutes. The temperature of the alcoholic perfume solution was maintained at about room temperature, i.e., 7212 F. The film was then removed from the alcoholic perfume bath and allowed to dry at room temperature until it was dry to the touch. The film was then smelled by several people and a fragrant rose aroma was prominently noticeable. The film was then allowed to stand at room temperature for 4 weeks and was again sniff-tested by several people. The rose fragrance was still pronounced. The same sample was then placed in a vacuum oven and heated to 200 F. for 24 hours. At the end of this time is was removed and 13 other odor comparison made. A fragrance was still noticeable, even under these severe conditions.

When a small segment of the film was scratched with a thumbnail an increase in fragrance was noted for a short period of time. This indicated a rupturing of the outer pore surfaces exposing more of the larger pore areas to the atmosphere.

It is believed that a typical pore impregnated with perfume would, if sufficiently enlarged dimensionally, appear to correspond to FIGURE 3 which is a hypothetical diagrammatic illustration of a cross-section of pore 56 having entrained within its inner Walls 62 a thin layer of capillarily bonded liquid perfume 60. This perfume is rather tightly bonded to the pore wall and only gradually diffuses over prolonged period of time. Pressure upon the pores, which are flexible to some degree, tends to distort the pore walls to cause the release of extra quantities of the perfume to the atmosphere.

While the above represents a preferred method for incorporating perfumes into the porous plastic compositions, it is to be understood that other methods may be used to accomplish the same result. In particular, it is contemplated as being within the scope of the invention to incorporate the perfume into the casting solution used to prepare the film or other shaped objects. This incor poration of the perfumes into the casting solution, while having the advantage of eliminating a separate perfume treating bath, has the disadvantage of requiring the perfume treated casting solution to be handled very carefully to prevent loss of the perfume by evaporation during the casting and subsequent treating steps. When the perfume is incorporated into the casting solution the amount used should be within the range of 0.1 to percent by weight. A typical illustrative method of incorporating the perfumes into film is suggested by Example VI below:

Example VI To the casting solution prepared in Example I, there was added 10 percent by weight of the following perfume.

Parts by Ingredient: weight Benzyl acetate Linalyl acetate 5 Benzyl alcohol 10 Peach aldehyde Cl4, 1 -amylcinnamic aldehyde 10 Linalool 5 Indole 10% 10 Methyl anthranilate 1 Benzyl salicylate Jasmone 3 Ylang-ylang 5 The solution was then cast onto a polished stainless steel sheet and was then immersed in water for 5 minutes at which point the film was stripped from the stainless steel plate and was further immerse-d in water for 60 minutes. The film was then removed from the water bath and allowed to dry for 10 hours at room temperature. The film was then tested using the same test methods described in Example V. After each series of tests, a lingering fragrance was still noticeable, although it was not quite as pronounced as in films prepared in accordance with Example V.

In a special embodiment of the invention, it is contemplated that special scented plastic objects may be made by utilizing ion exchange membranes of the type described in Mindick et al. U.S. 2,957,206. It is, of course, understood that in addition to using the anionic and cationic polyelectrolytes of the type disclosed in this patent, non-ionic polymers such as N-vinyl pyrrolidone polymers, polyacrylamides and the like may also be used. In accordance with the teachings of this patent, casting solutions are prepared, cast onto solid surfaces, and then heated to remove the solvent from the film. After the solvent had been driven from the film it is necessary that the film be contacted with certain organic liquids or mixtures of organic and inorganic liquids wherein degrees of porosity may be imparted to the film. These treatment steps are outlined in detail in the above described Mindick et a1. patent, pertinent portions of which are hereby incorporated in this disclosure by reference.

When it is desired to combine perfumes with such films, maximum porosity must be obtained by exaggerating the solvent treatment. The perfume may be incorporated into these films by either incorporating the perfume into the solvents used to after-treat the formed and dried films or it may be incorporated into the casting solution prior to their formation. The former technique is preferred.

Example VII A typical dried film produced in accordance with Example II of the Mindick et a1. patent was hydrated in 21 methanol solution for 48 hours to open the pores. At this time enough perfume of the type used in "Example VI was added to the alcoholic treating bath to provide a 1 percent solution. The film was allowed to soak for an additional /2 hour at which time it was removed and allowed to dry at room temperature. The film was scented to a high degree, but the scent disappeared after storage at room temperature for three weeks. This rapid disappearance of the fragrance indicated large uniform pores extending throughout the film.

Example VIII The procedure of Example VII was followed with the exception that after the film was dried at room temperature it was passed through a drying oven, the temperature of which was 250 F. This oven treatment lasted for only 60 seconds. The film was removed and after ten weeks of storage at room temperature, the fragrance persisted. This indicated that the surface of the pores had been closed, thereby trapping the perfume in the interior of the film.

Example IX The same procedure as was used in Example VII was again followed, except that the finished dried film was roller coated with a 10 percent solution of gamma butyrolactone in methanol. The coating on the film was allowed to set for 30 minutes and was removed by water washing. The film produced after drying was similar to that produced in Example VIII.

When the porous plastic objects, such as films, are produced in accordance with the teachings of Mindick et -al., and a non-ionic polymer such as poly-N-vinyl pyrrolidone is used, a slightly different technique may be utilized in preparing the scented objects. In particular, it is possible to treat these films with such materials as solvents of the type used to prepare the casting solutions, as well as monohydric and dihydric polyether alcohols. These treatments are applied to a solvent free dried film to open its pores.

The preferred swelling solvent is gamma butyrolactone. Other solvents which act to swell or expand the layer desired to be porous may be employed. Among them are, for example, acetic acid, acetone, dimethylformamide, tetrahydrofuran, cyclohexanone, and cyclopentanone. In order to control the swelling so that the product is not weakened, it is necessary in using some of the solvents that they be employed together with a liquid which either does not act to swell the layer or has less swelling action. Thus, the swelling solvent may be mixed with water as a regulator to control the degree of swelling. Methanol may likewise be mixed with the solvent to regulate the swelling. A preferred composition is composed of butyrolactone and methanol.

The residual solvent remaining in the initial film or formed object after drying may be employed to produce swelling, which takes place when the film or other object is immersed in methanol alone. The use of methanol alone is advantageous from the standpoint of operation and economy, but the resultant electrical resistance of lms so produced, is ordinarily slightly higher than that of films made with the preferred solvent combination. Low resistance is a desirable feature of films to be used, for example in a fuel cell as discussed hereinbelow. Expansion of a film layer is a function of temperature, and concentration and type of swelling solvent, so that it may be advantageous to heat the solvent or solvent mixture to a moderately elevated temperature, e.g., up to about 190 F.

It is preferred to immerse the film or other object to be made porous according to the invention, in the swelling solvent under conditions such that the necessary swelling will take place in a relatively short period of time under atmospheric conditions, i.e., within about 20 minutes. For example, a preferred swelling composition contains about 15 percent to 50 percent of a gamma 'butyrolactone and the balance methanol, and at times a surface active agent. Under atmospheric conditions, the maximum expansion may be obtained with such a mixture within several minutes.

The expansion with the foregoing composition may take place too rapidly, so that the film or plastic layers begin to shrink slowly and the electrical resistances increase. It is then preferred to decrease the expansion rate and increase the expansion time to provide for the necessary operating time while obtaining the best results. It has been discovered as part of the invention that swelling rate can be controlled when the swelling solvent is mixed with a hydrophilic non-ionic surface active agent. The preferred materials are polyhydric alcohols and their partial esters and ethers, especially the monohydric dihydric polyether alcohols. Polyalkylene glycols and monoesters and monoethers thereof are further preferred. The proportion of the surface active agent in the swelling composition is preferably about percent to 35 percent by weight of the composition. Where the composition is otherwise a mixture of swelling solvent and a liquid regulator of the degree of swelling, the surface active agent is added, for the most part, at the expense of the regulator.

After draining the solvent mixture, the expanded or swollen film or polymer layer is washed with either methanol or water. The swollen object, if a film, maybe somewhat soft and weak. After washing, the resulting film is hard and possesses good strength. It is ordinarily preferred to wash with water, which produces less shrinking in the washing process. In the case of 21 methanol wash, the film is subsequently treated with water for use in the hydrated form.

FUEL CELLS The films of the type prepared by treating the nondried casting solution with water are extremely valuable in the production of ion membrane fuel cells. These films have an extremely low resistance, are acid and alkali resistant, but most important, will not swell or shrink to any appreciable extent when going from the wet to the dry state and vice-versa. The films may also be cast or formed directly onto the porous electrodes used in the production of the fuel cells, thereby greatly simplifying their manufacture.

For a more comprehensive understanding of the porous films of the invention in their use in ion membrane fuel cells, the following discussion should be considered:

A typical fuel cell of the ion membrane is generally illustrated schematically in FIGURE 1. Specifically the fuel cell is composed of a chamber which is divided into two compartments l2 and 14, by a membrane 16. Positioned against the opposite faces 18 and 20 of the membrane are a pair of porous electrode members 22 and 24-. Compartment 12 is provided with an air inlet 26 whereas compartment 14 is provided with a hydrogen inlet 28. Suitable electrode connecting leads 30 and 32 are also provided for allowing current to be utilized in the operation of suitable electrical equipment such as a lamp 34. In a preferred embodiment the compartment 10 is fitted with a water outlet which removes the water formed during the conversion of the fuel into useful electrical energy. In operation, hydrogen is fed from a source, not shown, into inlet 28 while at the same time, air is admitted through the inlet 26. Both the hydrogen and air penetrate through the porous electrodes 18 and 20 and contact the surfaces of the membrane. On the hydrogen side, the electrons are given up, collected in the electrode and conducted to the electrical utilizing device 34. The hydrogen ions travel through the membrane to its other surface where they combine with the returning electrons in the presence of oxygen present in the air. As a result of this reaction, water is formed in Compartment 12 and may be readily withdrawn to the water outlet 36.

When the porous films are utilized in the fuel cells as described above, it is desirable that the average interior pore size be between 5 or 10 and 200 millimicrons, although it may range between 200 millimicrons to 1,000 microns. It is also important that the electrical resistance of these films does not exceed 15 ohms per sq. cm. at a thickness of 32 mils when equilibrated in a 0.15 N KCl solution.

The polypolar polymers used in producing films of this type should be either anionic or cationic. They should also be in the hydrogen or hydroxyl form. Thus, such polyelectrolytes as polystyrene sulfonic acid (H form), poly-(vinyl)benzene triethyl quaternary ammonium hydroxide and the like are suitable. They should have an average molecular weight of 10,000 or more. The hydrogen and hydroxyl ions act as charge carrier ions.

It is evident from the above discussion that the invention provides novel porous plastic compositions having utility and application in several areas of commercial importance. The perfume-containing porous structures have many applications in the field of packaging, novelty jewelry and the like, as well as being of extreme value in the production of ion membrane type fuel cells.

The invention is hereby claimed as follows:

1. A porous plastic film comprising a homogeneous dispersion of a water-insoluble, acid andalkali resistant thermoplastic polymer and a substantially linear waterdispersible polypolar polymer, said film being characterized by a plurality of pores extending throughout and perforating at least one dimension of said plastic film with the interior size of the pores being restricted near at least one point of their connection with an exterior surface of said film, said pores being further characterized as having average interior diameters substantially greater than the exterior surface openings of said pores and being thereby adaptable for slow release of liquids contained in said pores.

2. The film of claim 1 where the polypolar polymer comprises 10-60% by weight of said porous plastic film.

3. The film of claim 1 where the polypolar polymer is selected from the group consisting of anionic and cationic polyelectrolytes.

4. The film of claim 1 where the pores have an average interior size of between 5 millimicrons and 1,000 microns.

5. A porous plastic film having a thickness not greater than 20 mils which comprises a homogeneous dispersion of 4090% by weight of a water-insoluble, acid and alkali resistant thermoplastic polymer and 10-60% by weight of a substantially linear water-dispersible polypolar polymer, said film being characterized by a plurality of pores perforating the thickness of said film, with the interior dimensions of the pores being restricted near the perforated exterior surfaces of the film, said pores being further characterized as having average interior diameters substantially greater than the exterior surface openings of said pores and being thereby adaptable for slow release of liquids contained in said pores.

6. A porous plastic film of from 1 to 50 mils in thickness comprising a homogeneous dispersion of 70-90% by Weight of vinyl chloride polymer and 10-30% by weight of Water-dispersible vinyl pyrrolidone polymer, said film being characterized by a plurality of pores perforating the thickness of said film, with the interior dimensions of the pores being restricted near at least one of the perforated exterior surfaces of the film, said pores being further characterized as having average interior diameters substantially greater than the exterior surface openings of said pores and being thereby adaptable for slow release of liquids contained in said pores.

References Cited by the Examiner UNITED STATES PATENTS Van Der Kroon 264-45 McBurney 260-2.1 Hwa 260-21 Bechtold 18-57 Gorin 136-86 Justi 136-86 Mindick et al. 18-57 Wangner 117-1355 XR Jilge 117-1355 XR Leeds 167-94 X Hollowell 260-25 XR FOREIGN PATENTS WILLIAM D. MARTIN, Primary Examiner.

J. R. SPECK, Examiner.

Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,216,882 November 9, 1965 Charles A. Feldt et a1.

ied that error appears in the above numbered pat- It is hereby certif n and that the said Letters Patent should read as ent requiring correctio corrected below.

Column 3, line 15, for "In" read It column 6, line 61, for "diodide" read iodide "a Signed and sealed this 31st day of January 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Commissioner of Patents 

1. A POROUS PLASTIC FILM COMPRISING A HOMOGENEOUS DISPERSION OF A WATER-INSOLUBLE, ACID AND ALKALI RESISTANT THERMOPLASTIC POLYMER AND A SUBSTANTIALLYLINEAR WATERDISPERSIBLE POLYPOLAR POLYMER, SAID FILM BEING CHARACTERIZED BY A PLURALITY OF PORES EXTENDING THROUGHOUT AND PERFORATING AT LEAST ONE DIMENSION OF SAID PLASTIC FILM WITH THE INTERIOR SIZE OF THE PORES BEING RESTRICTED NEAR AT LEAST ONE POINT OF THEIR CONNECTION WITH AN EXTERIOR SURFACE OF SAID FILM, SAID PORES BEING FURTHER CHARACTERIZED AS HAVING AVERAGE INTERIOR DIAMETERS SUBSTANTIALLY GREATER THAN THE EXTERIOR SURFACE OPENINGS OF SAID PORES AND BEING THEREBY ADAPTABLE FOR SLOW RELEASE OF LIQUIDS CONTAINIED IN SAID PORES. 